Temperature sensing squib firing device

ABSTRACT

An atmospheric temperature sensing squib firing contrivance for igniting an explosive device at a specific outside temperature, comprising an atmospheric temperature sensor, a time delay safety function that prevents premature ignition, an enabling function that allows ignition when the desired input conditions are met, the ignition function, and an inside temperature sensor that stabilizes the circuits against changing ambient temperature of the explosive device.

United States Patent Brawn [54] TEMPERATURE SENSING SQUIB FIRING DEVICEJohn M. Brawn, Ridgecrest, Calif.

[73] Assignee: The United Stltes of America as represented by theSecretary 0! the Navy [22] Filed: May 28,1970

[21] Appl.No.: 41,437

[72] Inventor:

[52] U.S.Cl. ..l02/70.2R [51] lnt.-Cl. F42c 11/06, F42c 15/40, F42c19/06 [58] Field oiSearch ..l02/l9.2, 28, 70.2

[56] References Cited UNITED STATES PATENTS 3,351,016 11/1967 Simpson..102/70.2 3,559,582 2/1971 Hrzek ..l02/70.2

POSITIVE SUPPLY [451 June 27,1972

Primary Examiner-Benjamin A. Borchelt Assistant Examiner-Thomas B. WebbAttorney-R. S. Sciascia and Roy Miller [57] ABSTRACT An atmospherictemperature sensing squib firing contrivance for igniting an explosivedevice at a specific outside tempera- 1 ture, comprising an atmospherictemperature sensor, a time delay safety function that prevents prematureignition, an enabling function that allows ignition when the desiredinput conditions are met, the ignition function, and an insidetemperature sensor that stabilizes the circuits against changing ambienttemperature of the explosive device.

4 Claims, 1 Drawing Figure NEGATIVE SUPPLY PATENTEDJum I972 13. 672. 303

POSITIVE SUPPLY NEGATIVE SUPFLY I N VEN TOR.

JOHN M. BRAWN ROY MILLER ATTORNEY.

1 TEMPERATURE SENSING SQUID FIRING DEVICE GOVERNMENT INTEREST Theinvention described herein may be manufactured and used by or for theGovernment of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefor.

BACKGROUND OF THE INVENTION The present invention'comprises a squibfiring circuit used for igniting an explosive device. The firing circuitsenses an outside atmospheric temperature and causes ignition of theexplosive device at a predetermined atmospheric temperature. A necessaryfeature of the firing circuit is that ignition of the explosive devicemust be prevented for a predetermined time period to provide safeseparation from a launching vehicle such as an aircraft. A secondfeature is that ignition of the explosive device must also be preventeduntil the atmospheric sensor that initially can be warmer first senses acolder atmospheric temperature than the temperature at which ignition isto occur, i.e., it is intended that the explosive device incorporatingthe firing contrivance be launched initially into an environment that iscolderthan the atmospheric temperature at which ignition occurs.

BRIEF DESCRIPTION OF THE DRAWING The FIGURE is a schematic diagram ofthe firing circuit.

DESCRIPTION OF THE PREFERRED EMBODIMENT The squib firing contrivance isto be made an integral part of an explosive device that will be ejectedfrom a launching aircraft. The ambient temperature of the explosivedevice at the time of launch can be either warmer or colder than theatmospheric temperature of the environment into which it is launched. Atlaunch, the atmospheric temperature sensor is instantly exposed to theoutside environment that initially must be colder than the temperatureat which ignition of the explosive device is to take place. Ignitionoccurs when the atmospheric temperature warms to the desiredpredetermined value.

The circuit set forth in the FIGURE incorporates a battery that is anintegral part of the explosive device but whose sole purpose is toprovide power to this contrivance to effect ignition of the explosivedevice. The battery must be a special type with characteristics suitableto the particular application, there being two general classificationsthat are available. (I) The battery can be continuously active and thepower turned on to feed the firing contrivance by means'of switch13-that closes at the instant of launch. The positive side of thebattery is connected in series with the switch [3 through connector 11to the positive supply lead of the firing contrivance. The negative sideof the battery is connected through connector 12 directly to thenegative supply lead of the contrivance. Thus, full battery power isapplied to the supply leads of the contrivance at the instant of launch.(2) The battery can be a type that initially is inert but is made activeat the instant of launch. In this case, the switch 13' is omitted andthe positive side of the battery 10 is connected directly to thepositive power lead of the circuits through connector 11 and thenegative side of the battery 10 is connected directly to the negativesupply lead of the circuits through connector T2. In either case, poweris applied to the positive and negative supply leads of the circuits atthe instant of launch.

Connected between the positive and negative supply leads is I an outsideatmospheric temperature sensing thermistor T, in series with anadjustable potentiometer 14 which, in turn, is

' connected in series with a parallel combination comprising a Thecommon connection to the baseof transistor l5,-resisto'r R, and signalpoint A is by-passed through a capacitor C, to the negative supply lead.

Also connected between the positive and negative supply leads is acapacitor charging circuitcomprisinga resistor R in series with acapacitor-C, whose charge voltage having the time constant R C, appearsat signal point B. The common connection at signal point B is connectedto the collector of transistor 15.

The emitter of transistor 15 is connected through resistor R, to thenegative supply lead of the circuits and is also connected to theemitter of the unijunction transistor (UJT) l6 and to signal point C.

Also connected between the positive and negative supply leads of thecircuits is a series combination comprising resistor R in series withbase 2 of the UJT 16,. the internal inter-base resistance of UJT l6existing at base 1, in series with resistance R Base 1 of the UJT 16is'connected to signal point D and to the gate of a SiliconControlledRectifier (SCR) 17.

Also connected between the positive and negative supply leads of thecircuits is a squib 18 for igniting the explosive device, in serieswith'the anode-cathode portion of the SCR 17. The squib 18 is anintegral part of the explosive device and is external to the firingcircuit and is connected directly to the positive supply lead throughconnector 19 and to the anode of the SCR 17 through connector 20. Thecathode of the SCR 11 isconnected directly to the negative supply lead.

Operation of the firing contrivance is initiated by closing the switch13 or activating the battery 10, caused by launch from the aircraft, andsimultaneously exposing the atmospheric temperature sensing thermistorT, to the outside environment. Thus power is applied to the circuits atthe instant of launch and simultaneously the atmospheric temperaturesensing thermistor T,,, being exposed to the outside environment, startsrapidly cooling to the temperature that is colder than the desiredtrigger temperature. Response of the thermistor T to the sudden changein temperature from its initial ambient level to the differentatmospheric level is very rapid so that it starts accurately sensing theatmospheric temperature within a few seconds.

As power is suddenly applied to the positive and negative supply leadsat the instant of launch, capacitor C starts charging through resistor Rreaching a trigger threshold level at signal point B in a specified timeperiod determined by the time constant R C However, the capacitor Ccontinues to charge until such time as ignition of the explosive devicemay occur or until ultimately the charge voltage at point B reaches avalue essentially equal to the supply voltage. The charge voltage V, atpoint B constitutes a collector source voltage for transistor 15,conventionally designated V Full forward conduction through thetransistor (I cannot take place until the charge voltage V, at point Breaches its trigger threshold level. Excessive charge voltage at pointB, i.e., higher than threshold level, has no significant effect onfunctioning of the transistor 15. Therefore, heavy conduction throughthe transistor 15 is prevented as long as the charge voltage V, is lowerthan threshold level but can be enabled when V, at point B reaches or ishigher than threshold level.

The atmospheric temperature sensing thermistor T in series with theadjusting potentiometer 14, in series with an inside temperaturestabilizing parallel-series network comprising an ambient temperaturesensing thermistorv T in parallel with resistor R all in series withresistorR form an adjustable voltage dividing network whose output, V atpoint A principally varies in proportion to the outside atmospherictemperature. The signal, V at point A is therefore primarily related tosensing the atmospheric temperature. The atmospheric sensing thermistorT, has a negative temperature coefficient such that its resistanceincreases as the atmospheric temperature decreases. The higherresistance of T, associated with a lower temperature causes V at pointA, coupled through resistor R to be lower when the temperature is lower.The atmospheric temperature sense signal V, at point A is thereforeproportional to the outside temperature, i.e., conversely, V at point Arises when the outside temperature rises. The discrete signal, V,,, atpoint A for a given atmospheric temperature is determined by theadjustment of the variable tap of potentiometer 14. An actuation levelfor V at point A is thereby selectively related to a specificatmospheric temperature at which ignition of the explosive device isdesired. The signal V,,, while responding to outside temperature, ismodified in such a way as to stabilize the firing contrivance againstchange in the ambient inside temperature of the explosive device.

The stabilizing ambient temperature sensing thermistor T in parallelwith resistor R all in series with resistor R effects a correctivecomponent in the signal V,, at point A that satisfies the changingactuation level requirement at point A when the ambient temperature ofthe explosive device changes substantially. The needed compensation islumped for all of the temperature sensitive circuit components, e.g.,transistor 15, UJT l6 and SCR 17. The actuation level at point Aincreases as the ambient temperature gets lower, and vice versa. Thenegative coefiicient of thermistor T, causes the compensating componentof V, at point A to increase when the ambient temperature decreases. Thethermistor T, provides the basic compensation while the resistor Rconnected in parallel therewith linearizes the correction. Resistor Rbeing in series in the compensating network, limits the degree ofcompensation in the corrective component of V, at point A. Resistor R,therefore controls the slope of error, plotting atmospheric temperatureat which triggering occurs vs. ambient temperature of the total device.

Reiterating, the signal at point A is proportional to the atmospherictemperature, rising from a lower value when the atmosphere is initiallycolder than the desired trigger temperature, reaching the actuationlevel at point A at the same instant that the atmospheric temperaturehas warmed to the desired trigger temperature. The adjusted signal atthe moveable contact of the potentiometer 14 is coupled through resistorR to signal point A. Resistor R and capacitor C constitute an RF filterthat prevents stray signals from appearing at point A that would be dueto RF or radar radiations that the atmospheric temperature sensor may beexposed to in the outside environment.

The transistor 15 is configured in a general way as an emitter follower,that is, the emitter signal V, at point C follows or tends to beidentical to the temperature sense signal V,, at point A, conditionspermitting. However, V at point C can never exceed a value that isapproximately 0.6 volt less than V, at point A. This is due to aninherent voltage drop in the base-to-emitter junction of transistor 15.This is conventionally labeled V representing the drop when thebase-toemitter diode" is forward biased. The signal at point C thereforefollows the signal at point A with an approximate 0.6 volt offsetexpressed as: V, V, V This is true providing the capacitor charge signalV at point B has reached its threshold level or above. The signal V atpoint C is prevented from following the signal, V,,, at point A when thecharge signal V at point B has not reached threshold level. Thus, thetime delay charge signal V at point B enables or disables the transistor15 in a manner that allows triggering after a specified time intervalbut prevents triggering before the end of the specified time interval.The transistor 15 also provides an isolating function that preventsinteraction between the temperature sense signal, V at point A and thetime delay charge signal, V,,, at point B. Such isolation is necessaryto prevent the time-charge function from introducing error in thetemperature sensing function, and vice versa.

Since the emitter of transistor 15 is connected through signal point Cto the emitter of the UJT 16, the trigger actuation level, V,., at pointC is established by the critical emitter breakdown voltage V of the UJT16. The precise level of breakdown is established by the intrinsicstand-off ratio of the UJT 16. The critical point is a function of theseries circuit between the positive and negative supply leads comprisingresistor R in series with base 2 of the UJT 16, the inter-baseresistance of UJT l6 existing at base 1, in series with resistor R-,.The emitter to base 1 portion of the UJT l6 suddenly goes intoconduction at the instant that signal V, at point C reaches the criticalvalue of emitter breakdown V; of UJT 16. At the instant of emitterbreakdown in UJT 16, a heavy-current discharge path for the charge incapacitor C is formed, comprising the collector-emitter path ts) throughtransistor 15, the emitter-base-l path (133. through UJT l6, and mainlyresistor R However, the gate of the SCR 17 is in parallel with resistorR and therefore also becomes a branch of the high current discharge pathfor the charge in capacitor C,.

The charge signal V, at point B must have already reached its thresholdlevel before this chain of events can occur, i.e., the transistor 15must have been enabled for heavy conduction. At the instant of emitterbreakdown in the UJT 16, the voltage at point C drops to a value nearthe negative supply potential, which in turn forces the voltage at theemitter of transistor 15 downward thus enabling transistor 15 into astate of saturated conduction. This dumps the charge of the capacitor C,into the resistor R and the gate of the SCR 17.

The heavy discharge current causes an IR drop across the parallelcombination comprising resistor R and the gate of the SCR 17 so as toproduce a positive-going trigger pulse at signal point D. Since thispulse also appears at the gate of the SCR 17, the SCR 17 is turned on.The heavy current drawn through the squib 18 when the SCR 17 is in heavyconduction causes ignition of the explosive device. it is clear that thecritical breakdown value V, at point C reflects back and establishes theactuation level of V, at point A.

Assuming the worst case where the ambient temperature of the explosivedevice is warmer than the atmospheric temperature at which triggering isdesired, the atmospheric sense signal V, at point A, at time of launch,is already higher than the actuation level at point A. This is becausethe atmospheric sensor T is sensing the ambient temperature of thedevice at time of launch and has not yet had time to respond to theatmospheric temperature. Heavy conduction through transistor 15 cannotoccur because the capacitor charge signal V,, is near zero potential andthe transistor is not enabled. A path of light current flow does exist,however, because the base-emitter diode of transistor 15 is forwardbiased. The resulting voltage drop across resistor R is insignificantand does not threaten false triggering. Also the current is of smallenough magnitude that heating of the atmospheric sensing thermistor Tdoes not occur, T being a part of the current loop.

Immediately following launch, the charge signal V,, at point B starts torise and will reach threshold level in a prescribed time interval. Atthe same time, the atmospheric sense signal V, at point A is rapidlyfalling because the temperature sensor T has been exposed to theatmospheric environment. The thermal response of the atmospherictemperature sensing thermistor T,, must be fast enough that thetemperature sense signal V, at point A drops below actuation levelbefore the time delay charge signal V at point B can reach thresholdlevel. The time constant R C, of the charge signal V, is established byselective choice of the capacitor C, and resistor R, values. The timeconstant is made long enough to accommodate the thermal response of theatmospheric temperature sensor but at the same time short enough thatthe explosive device can function in its intended manner. For example,the charge time constant would be made 5 or 6 seconds if experienceshows the thermal response of the atmospheric temperature sensor Tallows the sense signal V, to go below actuation level within 2 or 3seconds. The time delay charge signal, V at point B is therefore thesafety factor because it enables or disables the transistor 15 and theatmospheric sense signal, V,,, at point A is the prime triggeringfactor.

Finally, the explosive device ignites when a specified amount of supplypower is gated into the firing squib 18. The positive-going pulse atsignal point D, as the UJT l6 triggers into conduction, causes theanode-cathode section of the SCR 17 to switch into heavy conduction andlatch. This causes essentially the entire supply voltage between thepositive and further function.

The switch 13 must be of a type that is actuated inertially or is springloaded and actuates as the explosive device clears its holder, if acontinuously live batter is used. Otherwise, the battery 10 mustinitially be inert, then become activated by an electrical meansreceived from the aircraft during launch, or by a mechanical meansinertially during launch from the aircraft.

It is expected that the ambient temperature of the explosive device willremain relatively constant after launch due to its mass andconfiguration. The thermal response of the stabilizing thermistor T,therefore does not need to be rapid like the requirement of theatmospheric temperature sensor. The

value of resistor R is chosen while adjusting and testing the accuracyof the atmospheric temperature sensor over a wide range of ambienttemperature change. Potentiometer 14 is adjust'ed to cause triggering ata specific desired atmospheric temperature which must be done before thefiring contrivance is introduced into the explosive device.

What is claimed is:

l. A temperature sensing firing device for use in an environmentcomprising;

switch means having an input and output;

time delay means operatively connected to said switch means for biasingsaid switch means off for a predeter mined time interval after saiddevice is released into a cold environment;

input signal means connected to the input of said switch means operativeto sense the environmental temperature and output a signal therefromthat varies in accordance with the environmental temperature;

said switch means producing an output pulse when switched to an oncondition; and

means operatively coupled to said switch means and responsive to saidoutput pulse therefrom for causing initiation of the firing device.

2. A temperature sensing firing device as set forth in claim 1 wherein;

said input signal means comprises a thermistor responsive to changes insaid environmental temperature.

3. A temperature sensing firing device as set forth in claim 2 andfurther including;

RF filter means connected between said input signal means and saidswitching means for filtering out RF signals in the environment.

4. A temperature sensing firing device as set forth in claim 1 andfurther including;

circuit stabilization means connected in series with said input signalmeans for compensating and linearising the output of said input signalmeans over a wide temperature range in the environment.

1. A temperature sensing firing device for use in an environmentcomprising; switch means having an input and output; time delay meansoperatively connected to said switch means for biasing said switch meansoff for a predetermined time interval after said device is released intoa cold environment; input signal means connected to the input of saidswitch means operative to sense the environmental temperature and outputa signal therefrom that varies in accordance with the environmentaltemperature; said switch means producing an output pulse when switchedto an on condition; and means operatively coupled to said switch meansand responsive to said output pulse therefrom for causing initiation ofthe firing device.
 2. A temperature sensing firing device as set forthin claim 1 wherein; said input signal means comprises a thermistorresponsive to changes in said environmental temperature.
 3. Atemperature sensing firing device as set forth in claim 2 and furtherincluding; RF filter means connected between said input signal means andsaid switching means for filtering out RF signals in the environment. 4.A temperature sensing firing device as set forth in claim 1 and furtherincluding; circuit stabilization means connected in series with saidinput signal means for compensating and linearising the output of saidinput signal means over a wide temperature range in the environment.